The present invention is concerned with a device which is used in a machine for processing sheet shaped workpieces such as by cutting, creasing or printing to convert these workpieces into blanks for packages which the machine discharging each of the processed sheets one after another into a pile with the device of the present invention including a fixed part mounted in a frame of the machine and a movable part or carriage having a fork-like configuration and being movable relative to the fixed part between a first position withdrawn from the path of the sheets forming the pile to a second position catching sheets being deposited on the pile to allow a previously formed pile of the sheets to be removed and an arrangement or means for shifting the carrier between the two positions.
As illustrated in FIG. 3, a device can be used for instance in so-called sheet delivery stations situated at the outlet or subsequent to a cutting press. As illustrated, the machine has a press P1 and sheets F gripped on a leading edge by a gripper bar B1 which is mounted on a pair of chains C3 is carried between the stations and from the last station such as P1 to a discharge station to be laid one after another in a pile E1 of sheets. When the pile is full, the prior art device allows the pile to be quickly removed in the following manner. During a short lapse of time beginning with the last sheet being applied on the pile and before the next sheet, an intermediate grid 45 was shifted over the top of the pile to an extended position 45' (shown in broken lines) to catch the next sheet being deposited thereon. During this period of time, the full pile can then be removed out of the delivery station. For the pile build-up, the station was equipped with a pile carrier provided with a movable table T1 having the shape of a vertically movable grid. With the view to insure a controlled delivery of the sheets, when the pile commences to build-up, the table T1 is lowered with each additional sheet arriving so that the upper level of the pile E1 will remain steady. It should be noted, in this discussion that the term sheets could also be the individual blanks in the event the delivery station is from a blank separator which would separate the linked together blanks of each sheet into individual blanks. For easy removal of the pile, the movable table T1 is mounted on an upper end of a vertical stay of shaft M1 which extends between two conveyor belts C1. As soon as the pile is full, the intermediate grid 45 is shifted to the extended position 45' to catch the next sheet as the vertical shaft lowers the movable table T1 downward till the lower most sheet of the full pile which is now pile E2 onto belts C1 to be removed in a direction toward the belt C2. After the belts C1 have moved the pile E2 off the table T1, it is again raised upward to engage the bottom sheet of the new formed pile E1 which is being temporarily formed on the intermediate grid 45.
In order to replace the support of the intermediate grid 45 by the support of the table T1, the prior art device has the grid elements of the table T1 pass between grid elements of the grid 45 to a position such as illustrated in dashed lines at T1'. In reality, the intermediate grid can be formed as a fork having prongs which form the supporting elements that will extend between the openings in the grid forming the table T1. Thus, once the table T1 assumes the position illustrated at T1', the pile E1 is lifted to allow the retraction and removal of the fork forming the intermediate grid 45. It should be pointed out, that this arrangement enables a removal of a pile without stopping the machine.
Other arrangements which are designed to intercept sheets as they are being laid down on top of a pile are disclosed in both Swiss Patent 359593 and German 1611776. In these designs, instead of an intermediate rigid grid, a flexible screen is unrolled over the pile allowing thus a new pile to be temporarily built up on the flexible screen as the pile therebelow is removed. As soon as the full pile underneath the flexible screen has been removed, the flexible screen is then rolled in backwards in order to be removed from underneath the new pile so that the new pile will then be able to take up a position on the vertical movable table like in the one described hereinabove.
Whether a rigid grid or flexible screen is used, their forward and backward movement have always been achieved up to now essentially by means of motor driven chains. However, on account of the relatively large range or distance to be covered which may be as large as 1200 millimeters and in view of the high speeds of production which will require the grid and screen movement of speeds up to 6 meters per second, the drive systems using such a chain design for moving forward and backwards are not only difficult to adjust but are a source of problems due to the chain breaking. Since the stopping and retraction cannot be easily controlled at the required points, it is also inaccurate.